It has been proposed to provide centralized charging functionality in all-IP (Internet protocol) networks, such as mobile communications networks in which a packet switched cellular network provides access for mobile users to services provided by external IP networks.
Diameter is an IETF (Internet Engineering Task Force) protocol that has been specifically designed for the Internet infrastructure. Diameter unifies authentication, authorization and accounting (AAA) transactions, The accounting related extension of the base Diameter protocol is likely to be used in networks which are all—IP (Internet Protocol) based for charging purposes.
There are two modes of charging. The first is on-line charging which is where the user effectively pre-pays for a data session and the second is off-line charging where a user is billed for a session after the session. Thus the first charging method is implemented by pay-as-you-go systems whereas the second method is implemented where the user is billed at regular intervals for calls which the user has made.
Currently, for a single session, it is only possible to have one method of billing. This is disadvantageous. For example, in a single session a user may access two or more services. However, a common method of billing will need to be used for these services. This could mean that a user would have to end a session for services using one billing method and start a second session for services using a second billing method. Clearly this is inconvenient and time consuming. Where the service in question is access to a particular resource, the access itself may require one billing method while the services provided via the resource may require a second billing method. This would not be possible with the current proposals. This is disadvantageous.
This is also the case for general packet radio services GPRS where each service is either prepaid or postpaid. This means that packet data protocol PDP contexts are either defined as prepaid or as postpaid, according to the charging profile defined in HLR for the subscriber.